Obsessional disorder of childhood is a severe psychiatric disturbance which is being increasingly recognized and treated. To date, a double-blind crossover trial of clomipramine has been shown effective in the treatment of this disorder. Clinical improvement does not correlate with plasma concentration of the drug, but does correlate significantly with decrease in platelet serotonin. A follow-up study of the 30 subjects who have, to date, participated in the drug trial is underway. Preliminary data indicate that 50% of the group are improved; the rest remain moderately to severely impaired. An epidemiological survey has just been completed of over 5000 high school students, in which obsessive compulsive symptomatology was rated. Follow-up interviews of high scorers on this questionnaire indicate that .3% of the adolescent population may have some form of this disorder, a rate far in excess of previous estimates.